Abstract

Background

Several recent studies have highlighted the important role of immunity-related molecules
in synaptic plasticity processes in the developing and adult mammalian brains. It
has been suggested that neuronal MHCI (major histocompatibility complex class I) genes
play a role in the refinement and pruning of synapses in the developing visual system.
As a fast evolutionary rate may generate distinct properties of molecules in different
mammalian species, we studied the expression of MHCI molecules in a nonhuman primate,
the common marmoset monkey (Callithrix jacchus).

Methods and results

Analysis of expression levels of MHCI molecules in the developing visual cortex of
the common marmoset monkeys revealed a distinct spatio-temporal pattern. High levels
of expression were detected very early in postnatal development, at a stage when synaptogenesis
takes place and ocular dominance columns are formed. To determine whether the expression
of MHCI molecules is regulated by retinal activity, animals were subjected to monocular
enucleation. Levels of MHCI heavy chain subunit transcripts in the visual cortex were
found to be elevated in response to monocular enucleation. Furthermore, MHCI heavy
chain immunoreactivity revealed a banded pattern in layer IV of the visual cortex
in enucleated animals, which was not observed in control animals. This pattern of
immunoreactivity indicated that higher expression levels were associated with retinal
activity coming from the intact eye.

Conclusions

These data demonstrate that, in the nonhuman primate brain, expression of MHCI molecules
is regulated by neuronal activity. Moreover, this study extends previous findings
by suggesting a role for neuronal MHCI molecules during synaptogenesis in the visual
cortex.